1. Field of the Invention
The present invention relates to a multi-piece solid golf ball with at least a four-layer construction. More particularly, it relates to a multi-piece solid golf ball which has a good, soft feel when hit with any type of club, ranging from a driver to a putter, and enables an increased flight distance to be achieved over a broad range in head speed (i.e., from low to high head speeds), and can thus provide good performance regardless of the head speed and the type of club used.
2. Prior Art
Golf balls having a variety of constructions are available today on the market. Of these, the golf balls generally used for competitive play are either two-piece solid golf balls having a rubber-based core enclosed within a cover made of ionomer resin or the like, or thread-wound golf balls comprising a solid or liquid center about which is wound a rubber thread which is in turn enclosed within a cover.
Most golfers of ordinary skill use two-piece solid golf balls because of their excellent flight performance and durability. However, these balls have a very hard feel when hit, in addition to which the rapid separation of the ball from the head of the club results in poor control. For this reason, many professional golfers and skilled amateurs prefer using thread-wound golf balls to two-piece solid golf balls. Yet, although thread-wound golf balls have a superior feel and controllability, their flight distance and durability fall short of those for two-piece solid golf balls.
Thus, two-piece solid golf balls and thread-wound golf balls today provide mutually opposing features, and so golfers select which type of ball to use based on their level of skill and personal preference.
This situation has prompted efforts to approximate the feel of a thread-wound golf ball in a solid golf ball. As a result, a number of soft, two-piece solid golf balls have been proposed. A soft core is used to obtain such soft two-piece solid golf balls, but making the core softer lowers the resilience of the golf ball, compromises flight performance, and also markedly reduces durability. As a result, not only do these balls lack the excellent flight performance and durability characteristic of ordinary two-piece solid golf balls, but they are often in fact unfit for actual use.
Various three-piece solid golf balls having a three-layer construction in which an intermediate layer is situated between a solid core and a cover have been proposed to resolve these problems. For example, JP-B 55077/1992 and JP-A 64-80377/1989 disclose golf balls in which the core is formed by enclosing a soft, relatively small inner layer (outside diameter, 24 to 29 mm; Shore D hardness, 15 to 30) within a hard outer layer (outside diameter, 36 to 41 mm; Shore D hardness, 55 to 65), so that the ball may exhibit both a long flight distance and a feel and control similar to that of a thread-wound ball. In another ball of this type, as described in JP-A 24084/1995,a soft intermediate layer is provided between the center core and the cover serving as the outermost layer of the ball in order to improve the feel without sacrificing the good flight performance and durability characteristic of solid golf balls.
However, the above-described three-piece solid golf balls are targeted primarily at golfers having a rapid head speed of at least 45 m/sec, and thus are necessarily suited to high-caliber players. When used by high head speed golfers, these balls are able to provide an increased flight distance and a good feel. Yet, when the same golf balls are used by low head speed golfers such as beginners, ladies,and seniors, the weakness of the force applied to the ball at the time of impact results in only a small amount of ball deformation and a greater dependence on the head speed to propel the ball. Thus an increased flight distance and a good feel are not obtained.
Moreover, with the rise in the golfing population, the attributes that golfers look for in a golf ball, such as flight performance, feel, control, and durability, have become more diverse and individualized. A need has been felt in the sport for the development of golf balls which are capable of accommodating differences in the ability and preferences of individual players, and which have, in particular, a low dependence on the head speed of the club.